Experiments > Gamedev

153: Shader Programming with The Book of Shaders and Godot

Shader programming is one of the things I have never touched in my life. And I always saw whoever makes shaders as some mythical programmer.

Since Monday I’ve been studying Shaders from scratch using The Book of Shaders and the Godot Engine documentation.

Shader programming is:

  • It’s hard.
  • It requires a lot of low level Math knowledge.
  • It’s fulfilling as soon you figure things out.

My First Shader Ever

The result is a pulsating gradient.

shader_type canvas_item;
void fragment() {
  COLOR = vec4(UV.x, UV.y, abs(sin(TIME)), 1.0);

Fence Problem

I spent the past 3 days cracking my head trying to understand chapter 5 – Shaping Functions, specifically the “fence problem”.

I finally understood it today and I can now even create variations of it. GLSL step and smoothstep really made me think and research a lot.

Variations of the Fence Problem with Godot


smoothstep(0.0, 0.01, abs(0.5-x + 0.5-y));

With this, we get exactly where they cut in the middle: 0.5-x + 0.5-y

Now wherever there was green, there’s black, because 1.0 (ok, green) has been changed to 0 (black):

return 1.0-smoothstep(0.0, 0.01, abs(0.5-x + 0.5-y));

Diagonal with step:
return 1.0 - step(0.01, abs(1.0-st.y - st.x));

Alternative easier to understand

  • return smoothstep(0.01, 0.0, abs(1.0-st.y - st.x));
  • y is being subtracted by 1 due to godot’s inverse Y, outside Godot: return smoothstep(0.01, 0.0, abs(st.y - st.x));

Notice that edge2 is 0.0, which means exactly where y & x meet, i.e:

  • y == x, y – x = 0, when x >= edge2, return 1.0


return smoothstep(0.0, 0.01, abs(0.5-x));

return 1.0-smoothstep(0.0, 0.01, abs(0.5-x));


return 1.0-smoothstep(0.0, 0.01, abs(0.5-y));


return 1.0-smoothstep(0.0, 0.01, abs(0.5-y)) + 1.0-smoothstep(0.0, 0.01, abs(0.5-x));


  • Godot


  • Gamedev
  • Shaders